David Walliams has conceded that exposing Mark Ronson's bare bottom to a 3,000-strong audience at a charity gig on Monday - and now the rest of the world via Youtube - was taking the uber producer "out of his comfort zone."

The embarrassing incident happened when Mark gamely joined the Little Britain comedian on stage during his slot at the Concert For CARE bash at the O2 Academy in Brixton.

Within seconds, David – in character as has-been kids' TV presenter Des Kaye – had tackled Mark to the ground twice and pulled down his trousers.

Afterwards, a repentant David said: "Mark is a cool, calm character. To put him in that position was out of his comfort zone."

Having your bum forcibly exposed to a large crowd will probably be out of most people's comfort zone.

"I offered to buy him a new suit," he added to Britain's Sun newspaper. "He said it wasn't necessary because he gets them free from Gucci."